1. Field of the Invention
The present invention relates to method for producing butanal (butyraldehyde) and, more particular, to a method for producing butanal using genetically engineered Streptomyces coelicolor. 
2. Description of the Related Art
Batch culturing and fermentation processes using microorganisms provide an efficient and cost-effective means of producing biochemicals and bioproducts. Using abundant non-anthropogenic feedstock as the starting material for producing these biomaterials is the goal of many scientists. It is estimated that over one billion dry tons of non-anthropogenic feedstock are available for use each year in the United States, almost half of which is available for under $40 a dry/ton.
As crude oil prices have risen, biochemicals and bioproducts have become increasingly attractive to the chemical and manufacturing world. Biochemicals and bioproducts such as butyraldehyde have many characteristics that make them better than most oil-based products, including the following: (a) lower greenhouse gas emissions from its production; (b) lower production costs due to starting materials; (c) fewer renewable starting materials are typically used; and (d) all the same physical properties as petroleum-based butyraldehyde. Butyraldehyde is used industrial applications in solvents and intermediates. The primary use for n-butyraldehyde, an intermediate formed using the subject technology, is as a chemical intermediate in producing other chemical commodities such as 2-Ethylhexanol (2-EH). 2-EH is widely used in plasticizers, coatings and adhesives. Other products requiring n-butyraldehyde include trimethylolpropane (TMP), n-butyric acid, polyvinyl butyral (PVB), n-butanol, and methyl amyl ketone. Smaller applications include intermediates for producing pharmaceuticals, crop protection agents, pesticides, synthetic resins, antioxidants, vulcanization accelerators, tanning auxiliaries, perfumery synthetics, and flavors.
With successful overproduction of butyraldehyde, a shift in use from chemical intermediates to conversion of butanol is predicted. Butanol or butyl alcohol (sometimes also called biobutanol when produced biologically), is a primary alcohol with a 4 carbon structure and the molecular formula of C4H9OH. Butanol is used as a solvent, as an intermediate in chemical synthesis, and as a fuel. Currently, n-butanol is being considered as an additive to gasoline. The current global market is about 350 million gallons per year with the U.S. market accounting for about 220 million gallons per year. Production of butanol for a gasoline additive could produce a demand of 72 million gallons a day in the United States.
Butyraldehyde is traditionally made by the hydroformulation of propylene. Cobalt catalysts were the original catalysts used, but newer rhodium catalysts are now being employed. Butyraldehyde can also be produced by the oxidation of butanol or hydrogenation of crotonyl. Butyraldehyde has never been successfully produced by an organism on an industrial scale.
Acetone-butanol-ethanol (ABE) fermentation with Clostridium acetobutylicum was once a widely used industrial fermentation process providing acetone, which was used to produce cordite. However, production of acetone from propylene has contributed to the downward spiral of ABE fermentation. ABE fermentation for production of butanol has gained interest since the 1980's as a use for gasoline additives, but limitations still prevent industrial scale production. Limitations associated with industrial scale production include: (a) low butanol yield from glucose (15-25%); (b) low reactor productivity (0.5 g/L·h); (c) low final concentrations of less than 15 g/L; and (d) expensive purification. As a result, ABE fermentation is not cost competitive with petroleum-based butanol production. Accordingly, there is a continued need for an inexpensive and effective method of producing both butanol and butanol precursors such as butyraldehyde and butyric acid.